Research Of A Wire-driven Propulsion Mechanism Inspired By The Seal Hind Flipper

With the increasing importance of marine environment exploration and resource development,Autonomous Underwater Vehicle(AUV)has become a focus of attention and research in the field of marine study.Specially,the power system(i.e.propulsion system),as the core unit to determine the performance of the underwater vehicle,has been the hotspot.Bionic propulsion has been favored in the field of underwater robot in recent 20 years due to its advantages of high speed,high efficiency,good mobility,and low noise pollution.Inspired by the hind flipper of seals,this paper proposes and designs a tail swing propulsion device based on wire driving principle and flexure hinge mechanism.The research has theoretical significance for the design of bionic propulsion,and also provides important reference for the development of bionic underwater vehicles.First of all,the structural characteristics and modes of locomotion of the seal’s tail bone were studied.It was confirmed that the seal’s pelvis has a large lateral expansion,which can easily drive the attached muscle.The phalanx of the hind flipper is crescent-shaped and can realize efficient propulsion in water.The tail of the seal performs an asymmetric periodic swing movement based on pelvic oscillation,and the hind flipper extends and contracts periodically along with swing of the tail.By imitating the shape and size of the tail of the harp seal in the literature,a swing propulsion device was proposed and designed based on wire driving principle and flexure hinge mechanism.Secondly,the swing trajectory equation of the tips of the hind flipper were obtained by using D-H parameter method,and the swing trajectory is preliminarily solved with the given assumed parameters.The influence of the swing angle parameters(swing angle,swing amplitude,and initial angle)of each equivalent link on the swing amplitude and unilateral swing limiting position of the propulsion device was analyzed.The results show that the swing amplitude and unilateral swing limiting position of the propulsion device vary linearly with the parameters of each swing angle.According to the analysis results of the influencing factors of the swing trajectory,the optimal swing angle parameters are obtained by the sequential quadratic programming method,and compared with the seal tail swing parameters under the same conditions,which verifies correctness of the optimization analysis.On this basis,units of the proposed swing propulsion device were designed in detail,involving the segmented flexure shell,bionic ankle joint,bionic flexure hind flipper,flexure hinge,and control unit.The simulation analysis of the hip flexure hinge shows that the rotation angle changes linearly with the increase of external force,and it is difficult to realize autonomous driving in the recovery stroke.The auxiliary spring was added to the hip joint,and the torque was analyzed to determine the stiffness of the auxiliary spring and the maximum torque of the actuator.A simplified hind flipper model was proposed to analyze and calculate the performance of the propulsion device.The results show that the propulsion force and torque of the propulsion device change periodically,and the peak value increases with the swing frequency.The mechanical efficiency of the propulsion device was calculated,and it is clear that the mechanical efficiency increases exponentially with the swing frequency.Based on the designed experimental prototype,experiments were carried out in air and water to verify the swing trajectory,and the experimental results are consistent with the theoretical analysis,which further verifies the correctness of the optimization analysis.The pool experiment platform was built to explore the changes of propulsion force and torque under different swing frequencies.The experimental results show that variation rule of the propulsion force and torque is consistent with the theoretical analysis,which verifies the correctness of the propulsion performance analysis.The performance improvement scheme of the propulsion device is explored by changing the mode of the propulsion device.The experimental results show that the extra propulsion force and torque of the propulsion device can be significantly reduced at the optimized propulsion mode,and thus the working performance of the propulsion device can be improved.